Sera from hyperimmunized mice will be used to characterize surface antigens coded by human chromosomes and to further localize the position of the genes coding for antigens on the respective human chromosomes. We will also determine whether the cellular immunoresponse to human histocompatibility antigens expressed in hybrid cells containing human chromosome 6 or part of human chromosome 6 is H2 restricted. The expression of H2 and HLA antigens will also be studied in hybrids between F9 mouse teratocarcinoma cells and either mouse cells derived from different mouse strains or human cells to determine whether in the undifferentiated hybrid cells the expression of H2 and HLA antigens is shut off and whether concordant expressions of mouse and human histocompatibility antigens occur in the differentiated hybrid cells. Syngeneic mice will also be hyperimmunized with somatic cell hybrids containing either chromosome 6 or the region p21 yields pter of human chromosome 6 and expressing HLA 3 and 7 for HLA 32, and their spleen cells will be fused with P3x63Ag8 mouse meyloma cells to obtain hybrids which produce antibodies against human histocompatibility antigens. This study should result in the selection of a series of hybrid clones producing monoclonal antibodies to different human histocompatibility antigens. In addition, we intend to study the cellular and humoral immunoresponse to Epstein-Barr (EB) virus nuclear antigen (EBNA) and surface antigens using somatic cell hybrids between mouse cells and Burkitt's lymphoma cells.